Top 40 Mainstream (often also called Mainstream Top 40) is an airplay chart from Billboard Magazine. It is often mistaken and confused with the Pop 100 Airplay charts (formerly Top 40 Tracks). Whereas the Top 40 Mainstream charts and Pop 100 Airplay both measure the airplay of songs played on Mainstream stations playing pop-oriented music, the Pop 100 Airplay (like the Hot 100 Airplay) measures airplay based on statistical impressions, while the Top 40 Mainstream uses the number of total detections. Arbitron sometimes refers to the format as Pop Contemporary Hit Radio.